Albert gould davis



(No Model.)

2 Sheets$heet l.

A. G. DAVIS.

RBGULATING ELECTRIC MOTORS.

No. 594,779. Patented Nov. 30,1897.

MAM/QM Qwi/Wmm I I 1 W 2 Sheets-Sheet 2.

(No Model.)

A. G. DAVIS. REGULATING ELECTRIC MOTORS.

Patented Nov. 30, 1897.

UNITED STATES PATENT @nrrcn.

ALBERT GOULD DAVIS, OF ASHINGTON, DISTRICT OF COLUMBIA.

REGULATING ELECTRIC MOTORS.

SPECIFICATION forming part of Letters Patent No. 594,779, dated November 30, 1897.

Original application filed November 17, 1896, Serial No. 612,493. Divided and this application filed J ly 1'7, 1897. Serial No. GPLQLZ. (N0 model.)

To aZZ whom it may concern:

Be it known that I, ALBERT GOULD DAVIS, a citizen of the United States, residing at Washington, in the District of Golumbia,have invented certain new and useful Improvements in Regulating Electric Motors, &c., (Case No. 10,) of which the following is a specification, taken in connection with the drawings hereto annexed.

In a prior application for Letters Patent, Serial No. 612,493, filed November 17, 1896, I have described, illustrated, and claimed certain improvements in the regulation of electric motors, &c., particularly those of the alternating-current type. In the present application, which is a division of the application above mentioned, I aim to cover certain improvements,specific under the broad claims of the said application, to be hereinafter described and claimed.

One of the present systems of alternatingmotor regulation is that known as the tandem multiple. By tandem in this connection is meant that arrangement in which a secondary winding on one motor feeds the primary of the next. The objection to such an arrangement is that it imports a large self-induction into the secondary circuit of the first motor and tends to destroy the torque. This I prevent by placing suitable condensers in the circuit in such a way that they set up waves of electromotive force which tend to correct in each secondary the lag due to self induction, which self-induction is principally due in practice to the primary winding of the next succeeding motor. I prefer to so adjust the condensers that the circuits are resonant for each particular speed desired, which tends greatly to increase the torque, but do not limit myself to a resonance condition, as it is in some cases sufficient if the self-induction is only partially neutralized. It is evident that I may replace the condensers in the arrangement by any other devices which will perform the same function, as electrolytic cells or other phase-advancing devices.

Another serious objection to the ordinary tandem-multiple system is that the same coils are obliged to act as secondaries and also as generating coils to furnish the current for the next succeeding motor. If they are given the low resistance usual in such members, the primaries of the next succeeding motors must also be given low resistance, and the current flowing becomes enormous. As this current has to pass through long connections and often through rubbing contacts, the 0 K loss outside the motors becomes large and the efficiency of the combination low, while the varying resistance of the rubbing contacts is with such heavy currents fatal to good regulation and even torque. It, 011 the other hand, the resistance is made high to overcome this defect, the motors must run with low efficiency when they are connected in multiple.

My invention therefore contemplates reducing the resistance of the secondary wind ings in the multiple condition, and while this may be accomplished in various ways I prefer to provide on each secondary member two windingsone of high resistance to act as a generating-winding and one of low resist ance to act as a short-circuited secondary. In this way I avoid the troubles mentioned above and also obtain an advantage at the time of passing from one connection to the other, as by closing the heavy windings of the first motor I am able to practically cut off all of the current from the other motors and avoid the necessity of shunting on the usual resistance.

To facilitate the closing of the heavy circuit and to avoid the necessity of bringing its current to the controller, I provide a mag netically -'operated switch on the induced member controlled in any desired way, as by the main controller, as more fully described hereinafter.

It will be seen that many of these improvements are not confined to tandem motor systems, but are of more general application.

I11 the drawings attached to this specification, Figure l is a diagram showing three motors and their controller with condensers arranged according to my invention. Fig. 2 is a section on the line a; as of Fig. 3, showing the induced member of one of the motors and the magnetic switch, the fine winding being Fig. 3 is a section on Figs. 4 to 9, incluomitted for clearness. the line y y of Fig. 2.

sive, are diagrams showing the connections of the system illustrated in Fig. 1 at various positions of the controller.

In Fig. 1 A, B, and C are the motors, geared in such a way that they may revolve together, as by being mounted to drive the same load. 1 have indicated this mechanical connection by the dotted line D.

A, 13, and C are the inducing members, respectively, wound in any preferred way with the usual primary windings a, I), and c.

A B and C are the induced members, wound with windings a b and 0 I have shown three-phase ring-windings for convenience of illustration, but may use any number of phases and any type of winding whatever, though if single phase is used some of the usual starting arrangements are necessary. In addition the induced members carry the windings (L3, Z), and 0 respectively, which are similar to those usual in the secondaries of induction-motors.

A generator E furnishes current which passes into the system through a transformer or transformers F, if desired, and to the controller G. This controller may be in its mechanical construction similar to the ordinary series-parallel controller and is shown only in diagram. Condensers A A", A If, B", and B of suitable capacity are provided.

The brushes of the controllers are numbered from 1 to 47, consecutively. \Vires $8, at, and 50 lead from the generator to the brushes 1, 2, and Contacts, as shown, are provided on the controller, and dotted lines at, 5, to 9' show the six different conditions of the controller corresponding, respectively, to the d iagrams Figs. 4 to 9, inclusive.

R, R and R are resistances. II is a source of current, preferably direct, and M, M and M are magnets controlling the heavy windings a, I), and respectively, as will now be described.

Figs. 2 and 3 show the induced members, which may be the stators, if preferred, though I have shown them as rotors. In the form shown the bars a are connected together at one end, as in the well-known Dolivo-Dobro wolsky winding, and at the other ends have notches 51, into which notches fits a conducting-ring 52, carried by a disk 53, sliding on but preferably insulated from the shaft of the motor and held back from the conductors by the springs 51. A magnet M serves to pull the disk, which in its inner portion should be of soft iron, against the conductors in order to close the winding. A ring 55 serves to introduce current to actuate the magnet, while the return circuit is shown as being through the shaft of the motor. This magnet M is one of the magnets M M M in Fig. 1 and serves to open and close the heavy induced windings, as may be desired. A stop 57 controls the motion of the disk and prevents it from being drawn out of the range of the magnets.

In the first position of the controller brushes 1, 2, and 3 rest on the contacts 1, 2, and 3, which are connected to contacts at, 5, and 0, as shown, whence the current travels by wires 58 59 G0 to the primarywinding a of the mo tor A. Supposing the motors to be at rest, an alternating current is induced in the winding (1 which travels by the wires (1." a a to the condensers A A" A, wires (t a a" to the brushes 7, 10, and 13, contacts 7, 10, and 13, cross connections, contacts 16 17 18, brushes 16, 17, and 18, and wires a a a to the primary windings I) of the motor 1). In the same way the CLIIlGlllillldtlCGt'l in the winding b on the induced member 13 of the motor B flows by wires Z) U Z) to the condensers B 13 B, wires 11 b Z), brushes 19 22 25, contacts 19 22 25, cross connections, contacts 28 29 30, wires D 7), and I) to the primary winding 0 of the motor 0. The current thus induced in the secondary winding 0 of the motor 0 travels by wires a e 0 to resistances It R R wires c c c, brushes 31 32 33 to the contact 31, the common point of the three-phase system. It is now evident that each of the meters is producing a starting torque and that the system will. accelerate to a speed approaching one-third of its normal speed; but as the resistances are interposed in the secondary of the last motor the slip will be large, and the torque also large at low speeds, and the motors will run slowly with fair efficiency and great starting torque, which torque is increased by the action of the condensers. Each rotor slips considerably and has induced in it a currentof a frequency which is a function of the slip, as is usual in tandem systems. The condensers are preferably adjusted to make the whole system resonant or consonant at a low speed. The capacity required is found by calculation in the well-known way. Fig. 1 shows the arrangement in diagram and needs no explanation. The motors being thus started, the controller is moved to the position -1 when the brushes 8, 11, 1-1, 20, 2 3, and 20 bear on the contacts 7, 10, 1:3, 19, 22, and 25, respectively, and the brushes 31- 35 3b bear on the contact 31. This evidently cuts in a larger capacity in each circuit and cuts out some of the resistance, and the system is adjusted for a higher speed. In the same way at the position a the whole capacity is in circuit, and the winding c is shortcireuited. At this notch the motors will come to very nearly onethird of their normal speed and will run with great efficiency, and the position is therefore suitable for climbing heavy grades when the motors are placed on street-ears.

At the position 5 (shown in diagram in Fig. 5) the secondary of the motor 0 is opened by the brushes 31 to 39 coming off the contact 31. Otherwise the connections are the same. The condition of resonance bein thus destroyed, and the secondary of the last metor being open, a small current only will. How in the intermediate circuits, by which term I include all those circuits which lead IIC from the secondary of one motor to the primary of the next. This is not a running position.

At the position 6 the motors B and G are out out and the brushes 40 4:1 42, attached to the wires (L a to, bear on the contact 40. The motor A is thus connected to line with its fine winding short-circuited. It will therefore slip considerably, owing to the resistance of the fine winding, but it will nevertheless speed up, and its normal or theoretical speed is now that dueto theline frequency.

In the position 7 the brushes 46 4,7 bear on the segment 46 and a current flows from the source H through the magnets M M M which attracts the disks 53 and closes all of the heavy windings; but as only one of the motors is supplied with current the others do not act. The connections are as indicated in Fig. 7. These two last positions are to be used as running positions only when high speed at low torque is Wanted, as on a streetcar running on a level or down a slight grade.

The positions 8 and 9 give the multiple connections. At 8 (represented in diagram in Fig. 8) the current enters, as before, at the brushes 1 2 3, but the segments 1 2 3 are cross-connected to the segments a 5 6 16 17 18 and 28 29 30", as shown, connecting all of the motors in multiple. The high-resistance secondaries are all closed by the brushes 3? to 45 bearing on the contact 37. The motors thus tend to run at the speed due to the line frequency, but as their secondaries have high resistance they slip considerably and have a heavy torque, and the speed is considerably less than the theoretical.

In the position 9 the brushes 4,6 and 47 bear on the segment 46 and the low-resistance secondaries are again closed,which gives the final running position.

It will be seen that I thus provide an efficient system of motor control, in which the machines will start and run with a large torque, and that I avoid the objections mentioned above.

I have illustrated my invention with special reference to three-phase systems,which I consider preferable for ordinary work, but it is evident that my improvements are applicable to any alternating system whatever.

I do not restrict myself to the various forms and connections shown and described, but claim as my invention and desire to secure by Letters Patent-- I claim- 1. The combination of a plurality of motors coupled in tandem, with phase-advancing devices adapted to neutralize, in whole or in part, the self-induction of the intermediate circuits, substantially as described.

2. The combination of two alternating-cur rent motors with an intermediate circuit lead ing from the secondary of one motor to the primary of the next, and a condenser soconnected as to regulate the phase relation between the current in the external circuit and the current in the intermediate circuit, substantially as described.

3. The combination with two alternatingcurrent motors connected in tandem, of a con denser in each lead of the intermediate circuit.

4. The combination with two alternating current motors connected in tandem, of an adjustable condenser in each lead of the inter;- mediate circuit.

5. The combination with a plurality of alternating-current motors, of condensers, and a switch so adjusted and connected as to connect the motors in tandem,with the condensers in the intermediate circuits, vary the capacity of the condensers, and finally connect the motors in multiple.

6. The combination with a plurality of alternating motors, of condensers, means for connecting said motors in tandem and in multiple, and means for inserting the condensers in the intermediate circuits when the motors are connected in tandem.

7. The combination with a plurality of alternating motors, of condensers, means for connecting said motors in tandem and in multiple, means for inserting the condensers in the intermediate circuits when the motors are connected in tandem, and means for varying the resistance of the induced members of the motors.

8. The combination with a plurality of alternating motors, of condensers, means for connecting said motors in tandem and in multi ple, means for inserting the condensers in the intermediate circuits when the motors are connected in tandem, and means for reducing the resistance of the induced member of the first motor while in the multiple position below what it was while in the tandem position.

Signed at lVashington, District of Columbia, this 17th day of July, A. D. 1897.

ALBERT GOULD DAVIS.

lVitnesses:

W. H. DAVIS, J. E. HOUKEN. 

